In a prior art fluid machine, as disclosed, for example, in Japanese Patent No. 2540738, a compressor device for a vapor compression refrigerating cycle is commonly used as an expansion device, and the compressor device is used as the expansion device when energy is collected by Rankine cycle.
In the above fluid machine, the compressor device is used as a compressor for air conditioning operation, wherein the compressor device compresses the refrigerant in the refrigerating cycle. The compressor device is used as an expansion device, when the air conditioning operation is stopped, wherein superheated gas-phase refrigerant generated in the Rankine cycle by use of the waste heat from the engine is supplied to the fluid machine. The refrigerant is expanded in the fluid machine to operate as the expansion device and energy generated by the expansion device is applied to the engine.
In the above prior art fluid machine, in which the compressor device is also used as the expansion device, the fluid machine can be used as the expansion device only during a time period in which the air conditioning operation is not necessary. As a result, the prior art fluid machine can not most efficiently improve a fuel consumption ratio for the engine.
The inventors of the present invention proposed a fluid machine in a prior Japanese patent application (JP 2003-82760), in which a compressor device 140 and an expansion device 150 are independently provided and connected to each other by a driving shaft 111, so that the expansion device 150 for collecting and utilizing the waste heat can be operated, irrespectively whether or not the compressor device 140 is operated for an air conditioning operation.
According to the above proposed fluid machine, the compressor device 140 is a variable capacitor type (a swash plate type) compressor, and a discharge amount of the compressor device 140 is adjusted to become zero, when the air conditioning operation is not necessary. Accordingly, a resistance of the compressor device 140 is reduced when the expansion device 150 is in its operation.
In the above proposed fluid machine, although the discharge amount of the compressor device 140 is adjusted to become zero to reduce the resistance by the compressor device 140 to the expansion device 150, mechanical loss due to friction in sliding portions of a capacitor varying mechanism (such as, a swash plate 140B in a swash plate chamber 140A, and shoes 140C) can not be avoided. As a result, the expansion device 150 can not sufficiently collect and utilize the waste heat.